Field
This disclosure generally relates to lighting fixtures using a passive cooling technology and more particular to a modular in-grade luminaire with heat pipes.
Description of the Related Art
Conventional in-ground or in-grade lighting fixtures are typically buried all or partially below ground level and include a light emitter that illuminates up from below ground level. They can be buried in the earth or covered by hardscape such as concrete, asphalt, wood, pavers, tile, etc. The fixtures are typically used to illuminate walls, columns, flags, trees, signs or a pathway.
One type of in-grade lighting fixture generally comprises a housing and lens made of glass or other rigid and transparent material that is attached to an opening in the top of a housing. The housing contains various components including the light emitter that is arranged to emit light through the lens and electrical components that are used to power and operate the light emitter. When the light fixture is installed in-grade, the housing is typically below ground level and the lens is left uncovered so light can shine up through it. The electrical components can include a power supply, power converters, transformers, and mounting hardware for the light emitter. To hold all of these components, the housing can extend relatively deep into the ground (i.e. 14 to 16 inches).
During installation of these types of light fixtures, a hole is typically dug for the housing, the housing is placed in the hole and the hole is back filled around the housing. Any hardscape is then installed around the lens, leaving the lens uncovered.
In-grade light fixtures can have an optical chamber that contains the light emitter (lamp), with the optical chamber arranged in the housing so that light from the lamp emits through an upper housing opening. One disadvantage of conventional optical chambers is that condensation can develop inside the chamber through the heating and cooling of the lamp. These types of fixtures also have ballasts that contain electronic components such as transformers and capacitors. These ballasts can also develop condensation during heating and cooling that can cause failure or reduced life of the components.
With the advent of the efficient solid state lighting sources, it is more common for light emitting diodes (LEDs) to be used as the light source in lighting applications. LEDs have certain characteristics that make them desirable for many lighting applications that were previously the realm of incandescent or fluorescent lights. Incandescent lights are very energy-inefficient light sources with a vast majority of the electricity they consume being released as heat rather than light. Fluorescent light bulbs are more energy efficient than incandescent light bulbs, but are still relatively inefficient. LEDs by contrast, can emit the same luminous flux as incandescent and fluorescent lights using a fraction of the energy.
Modern lighting applications often demand high power LEDs while reducing the size of the LED package. High power LEDs can draw large currents, generating significant amounts of heat that must be managed. There can be issues in using high power LEDs as a light source for in-grade light fixtures. In-grade light fixtures typically enclose the light source from exposure to the surrounding environment, such as water or soil, which could damage the light source and/or other electronic components within the in-grade light fixture. In-grade light fixtures retain heat generated from the light source and/or other electronic components and can have difficulty in dissipating the heat to the earth or surrounding hardscape. This results in power output limitations for the LEDs of approximately 15 W in order to maximize the light emitted by the LEDs.
The most common problems resulting from the operational temperature of the in-grade light fixture becoming too hot include reduced light emission from the LEDs and failure or reduced life of the LEDs and/or other electronic components.
Conventional in-grade light fixtures are typically installed in settings where replacement of an in-grade light fixture is labor intensive and could require demolition. In other conventional light fixtures one or more ballasts can be included inside the housing, which can increase the overall size of the light fixture. Conventional light fixtures also do not provide flexibility in the placement of ballasts or other internal components to allow the light fixture to be configured to meet space constraints during installation. It is desirable to not have to remove and replace the entire in-grade light fixture with an updated in-grade light fixture, and instead install updated electronic components within existing in-grade light fixtures. As such, the internal spacing of the installed in-grade light fixture is limited and any new or updated cooling devices that are installed to assist with heat dissipation must be configured to meet the space constraints of previously installed in-grade light fixtures.